MATHEMATICS TEXTBOOK FORM 5

CHAPTER 6 Ratios and Graphs of Trigonometric Functions

Solution:

(a) From the graph, amplitude = 0.6, therefore a = 0.6

period = 5 seconds, therefore 36b0° = 5

b = 72

there is no movement of going up or down the x-axis, therefore c = 0

Hence, a function that models the airflow in normal respiratory cycle shown as the graph
is y = 0.6 sin 72x.

(b) y = 0.6 sin 72x

When x = 7, y = 0.6 sin (72 × 7)

y = 0.35

Hence, the airflow velocity is 0.35 litre per second when the time is 7 seconds.

Self Practice 6.2c y

1. The graph on the right shows the depth of water 12
recorded in a dockyard. Depth (feet)
(a) If y represents the depth of water, in feet, CHAPTER 69
and x represents the number of hours after
midnight, use the function in the form of 6
y = a cos bx + c to model the depth of water
shown as the graph. 3
(b) At what time will the water be the deepest?
0 x
6 12 18 24

Number of hours after midnight

2. The diagram on the right shows the view from the Light ray
top of a lighthouse and the coast. The beacon of
the lighthouse sends out a light ray as shown in Beacon of s
the diagram. When the beacon rotates, the light ray lighthouse Coast
moves along the coast at an angle, x.
(a) Write a function for the distance s. x
(b) State the amplitude and the period of the 500 m
function.
y
3. The graph on the right depicts the water level 4.0
recorded at a port. It is given that y represents the
water level, in m, and x represents time, in hours. 1.8
State the trigonometric function of the graph in the
form of y = a sin bx + c.

0 x
6 12 18 24

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Summary Arena

Unit circle Corresponding reference angles

y sin q = y-coordinate Let a be a corresponding reference angle
y Quadrant II
1 (x, y) cos q = x-coordinate
1θ y θ a = 180° – q
–1 Ox 1 x tan q = y-coordinate α O x sin q = + sin a
x-coordinate cos q = – cos a

–1 Sine, tan q = – tan a
Cosine
Signs of values of sin q, and y Quadrant III
cos q and tan q θ a = q – 180°
Tangent
y
α O x scions q = – sin a
q = – cos a

tan q = + tan a

Quadrant II Quadrant I y Quadrant IV
(sin +) (All +)
x a = 360° – q
Quadrant III θ
(tan +) Quadrant IV O α x scions q = – sin a
(cos +) q = + cos a

tan q = – tan a

Graphs of sin x, cos x and tan x for 0° < x < 360°

CHAPTER 6 Shape of graph y = sin x y = cos x y = tan x

y y y
1 1 1

0 x 0 x 0 x
90° 180° 270° 360° 90° 180° 270° 360° 90° 180° 270° 360°

–1 –1 –1

Maximum value 1 1 ∞
Minimum value –1 –1 – ∞
x-intercept 0°, 180°, 360° 90°, 270° 0°, 180°, 360°
y-intercept 0 1 0

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CHAPTER 6 Ratios and Graphs of Trigonometric Functions

Reflection

At the end of this chapter, I can

make and verify conjecture about the value of sine, cosine and tangent for angles
in quadrants II, III and IV with the corresponding reference angle.

determine the value of sine, cosine and tangent for angles in quadrants II, III and
IV based on the corresponding reference angle.

determine the angle when the value of sine, cosine and tangent are given.

solve problems involving sine, cosine and tangent.

draw graphs of trigonometric functions y = sin x, y = cos x and y = tan x for
0° < x < 360°, hence compare and contrast the characteristics of the graphs.

investigate and make generalisations about the effects of changes in constants
a, b and c on the graphs of trigonometric functions:
(i) y = a sin bx + c
(ii) y = a cos bx + c
(iii) y = a tan bx + c
for a . 0, b . 0.

solve problems involving graphs of sine, cosine and tangent functions.

MINI PROJECT CHAPTER 6

Radio broadcasting is an example of electronic communication that can be found
today. Sounds like music and voices that we hear from the radio are broadcasted in
the form of waves. In the case of AM radio, sound is transmitted through amplitude
modulation whereas for FM radio, sound is transmitted through frequency modulation.
In groups of four, do a brief report that explains the difference between
amplitude modulation and frequency modulation based on the characteristics of the
graphs of the trigonometric functions that you have learnt. You are encouraged to use
appropriate graphs, tables, and mind maps to present your group report.

AM

FM

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Extensive Practice Scan the QR code or visit
bit.do/QuizE06 for interactive quiz

UNDERSTAND

1. State the relationship between each of the following trigonometric functions with its

corresponding reference angle.

(a) tan 154° (b) sin 234° (c) cos 314°

2. Determine the value of each of the following based on its corresponding reference angle.

(a) cos 116° (b) tan 211°389 (c) sin 305.6°

3. Given that tan q = – 0.7265 and 0° < q < 360°, calculate the angle q.
4. Sketch the graph of y = cos x for 90° < x < 270°.

MASTERY

5. State the maximum and minimum values of the graph of function y = 3 sin 2x – 1 for
0° < x < 360°.

6. In the diagram on the right, q = 150° and a = b. Determine the y x
αθ
values of β
(a) cos a
(b) tan b

7. The diagram on the right shows a piece of wood with a length 8m
θ
of 8 m leaning against a vertical wall. The horizontal distance
from the wall to the wood is 6 m. Calculate the value of sin q. 6m

CHAPTER 6 8. Sketch the graph of the function y = 3 sin 2x + 1 for 0° < x < 360°.

9. The diagram on the right shows a graph of a y x
trigonometric function for 0° < x < 360°. 1 360°
(a) Write the trigonometric function. 0 (m, 0.5)
(b) State the value of m.
180°
–1

10. The diagram on the right shows a graph obtained Current (ampere)
on the screen of an oscilloscope when a supply of 3
alternating current is connected to it.
(a) Which type of trigonometric functions is 0 Time
represented by the graph? 0.4 0.8 1.2 1.6 (seconds)
(b) State the amplitude of the current.
(c) State the period of the current. –3

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CHAPTER 6 Ratios and Graphs of Trigonometric Functions

CHALLENGE y (1, 0)
A x
11. A regular hexagon is drawn in a unit circle as shown in the
diagram on the right. If one of the vertices of the hexagon is at O
(1, 0), determine the coordinates of vertices A, B and C.

BC

12. Your school band performs on the field. Band y Original Field boundary
members make a circular formation with a position, (5, 0)
diameter of 10 m. Assume that you are one of 300°
the members and your original position is 9 m O x
from the field boundary. After you have moved,
your new position is as shown in the diagram 9m
on the right. If you are required to move to the New position
field boundary from your new position, what
is the shortest distance, in m, would you walk
through?

13. The table below shows the height of Ming Seng’s position from the horizontal ground
as he rides on the Ferris wheel.

Time (minutes) 0 2 4 6 8

Height (m) 20 31 20 9 20

(a) Based on the table, state the type of trigonometric function that it can represent.
(b) Hence, if y is the height of Ming Seng’s position from the horizontal ground, in m,

and x is the time in minutes, sketch the graph and state the trigonometric function
representing the information above.

14. The diagram on the right shows a security camera in front s x Security CHAPTER 6
of a fence of an apartment. The camera is mounted on a Fence 5m camera
pole located 5 m from the midpoint of the fence. Write a
trigonometric function that expresses the distance, s, in m, Midpoint of the fence
along the fence from its midpoint in terms of x.

EXPLORING MATHEMATICS

Do you know that trigonometric functions can be applied when programming a character
which is jumping in a computer game?
Try to relate the movement patterns of computer game characters with trigonometric
functions. Get the relevant information from legitimate sources such as interview a
programmer, refer to a reading material or others. Write a short journal on
• the characteristics of trigonometric functions,
• the use of trigonometric functions in computer games,
• two other examples of real-life applications involving trigonometric functions.

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7CHAPTER Measures of Dispersion
for Grouped Data

What will you learn?
• Dispersion
• Measures of Dispersion

Why study this chapter?
Statistical analysis such as measure of dispersion is widely applied in various fields,
including medicine, agriculture, finance, social science and many more. The career fields
that apply statistical analysis include biometrics, actuarial science and financial analysis that
use big data to obtain statistical values, and hence represent the data in statistical graphs.

Do you know?
William Playfair (1759-1823) was a Scottish economist
who used various common statistical graphs in his book,
The Commercial and Political Atlas, published in 1786.

For more information:

  bit.do/DoYouKnowChap7

CHAPTER 7 WORD BANK grouped data data terkumpul
histogram histogram
196 cumulative histogram histogram longgokan
cumulative frequency kekerapan longgokan
KPM quartile kuartil
ogive ogif
statistical investigation penyiasatan statistik
percentile persentil
frequency polygon poligon kekerapan

Number of Daily Cases of Covid-19 in Malaysia

260 Phase 1 Phase 2 Phase 3 Phase 4
240 MCO MCO MCO MCO
220
200 18 Mar – 31 Mar 1 Apr – 14 Apr 15 Apr – 28 Apr 29 Apr – 12 May

Number of cases180
160
CHAPTER 7140
120 Date (2020)
Source: Ministry of Health Malaysia, July 2020
100
80
60
40

20
0

The outbreak of the Covid-19 pandemic in early 2020 has forced Malaysian to

adjust to a new normal. The swift and efficient action taken by the authorities in
tackling the pandemic has helped Malaysia to control the increasing number of
patients infected by the virus. Malaysia is successful in flattening the curve of the
number of daily infected cases by issuing the Movement Control Order (MCO). In
your opinion, how will the shape of the graph be if MCO has not been implemented?

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7.1 Dispersion

How to construct histogram and frequency polygon?

In Form 4, you have learnt about the ways to interpret the Construct histogram and
dispersion of ungrouped data based on the stem-and-leaf plots frequency polygon for a
and dot plots. We can observe the dispersion for a grouped data set of grouped data
by constructing histogram and frequency polygon. Prior to that,
you need to know the class interval, lower limit, upper limit, Info Bulletin
midpoint, lower boundary, upper boundary and cumulative
frequency that can be obtained from a frequency table. Class interval is the range
of a division of data.

MIND MOBILISATION 1 Group

Aim: To recognise the lower limit, upper limit, midpoint, lower boundary and upper
boundary of a set of data.

Steps: 8 10 4 7 1
5 2 8 11 4
The data shows the amount of daily pocket money in 5 7 15 3 4
RM, received by 20 pupils on a particular day. 14 12 7 11 9

1. Identify the smallest data and the largest data.

2. By referring to the data, group the data into 3, 4, 5 or 6 parts in sequence. For
example, a group of three uniform parts means 1 – 5, 6 – 10 and 11 – 15.

3. By using the tally method, choose and insert the data according to the parts of the
group.

4. Based on each part of the data, determine
(a) the lower limit (the smallest value in a part of the data) and the upper limit (the
largest value in a part of the data),
(b) the midpoint of each part of the data,
(c) (i) the middle value between the lower limit of a part and the upper limit of
the part before it,
(ii) the middle value between the upper limit of a part and the lower limit of
the part after it.

CHAPTER 7 5. Complete the frequency table with the results of steps 3, 4(a), 4(b), 4(c)(i) and
4(c)(ii) as shown below.

Pocket money Frequency Step 4(a) Step 4(b) Step 4(c)
(RM) (i) (ii)
Lower limit Upper limit Midpoint

Discussion:
Discuss and write down the definition to determine the lower limit, upper limit, midpoint,
lower boundary and upper boundary of a set of data.

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CHAPTER 7 Measures of Dispersion for Grouped Data

The results of Mind Mobilisation 1 show that;

Size of class interval Lower boundary

1 2= 1 2= of
Largest data value – Smallest data value Upper limit of it + Lower limit   
Number of classes the class before 2  the class

Lower limit is the smallest value and upper Upper boundary
limit is the largest value of a class. 1 2=
Upper limit of Lower limit of
1 2Midpoint = the class + the class after it
Lower limit + Upper limit
2 2

Example 1

The data on the right shows the 153 168 163 157 i – Technology
heights, to the nearest cm, of a 158 161 165 162
Scan the QR code or
group of Form 5 pupils. 145 150 158 156 visit bit.do/WSChap7i
to explore ways to
(a) Determine the class intervals 166 163 152 155 organise raw data in
for the data, if the number 158 173 148 164 frequency table by using
of classes required is 6. spreadsheet.

(b) Construct a frequency table based on the information in (a).

Hence, complete the frequency table with the lower

limit, upper limit, midpoint, lower boundary and upper

boundary.

Solution:

(a) The largest data is 173 and the smallest data is 145.
If the number of classes is 6, then the size of each class interval

= 173 – 145 Size of class interval
6
1 2=
= 4.7  5 Largest data value – Smallest data value
Number of classes

Therefore, the class intervals are 145 – 149, 150 – 154, 155 – 159, 160 – 164,
165 – 169 and 170 – 174.

(b) Height Frequency Lower Upper Midpoint Lower Upper
(cm) limit limit boundary boundary
149 147
145 – 149 2 145 154 152 144.5 149.5 CHAPTER 7
159 157 149.5 154.5
150 – 154 3 150 164 162 154.5 159.5
169 167 159.5 164.5
155 – 159 6 155 174 172 164.5 169.5
169.5 174.5
160 – 164 5 160

165 – 169 3 165

170 – 174 1 170

For a grouped data in uniform class intervals, the size of class interval can be calculated using
two methods.

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Method 1: The difference between Method 2: The difference To determine the size of
the lower limits or the upper limits between the upper class interval, avoid using
of two consecutive classes. boundary and the lower lower and upper limits of
boundary of a class interval. a class. For example, for
Size of class interval of the first class interval 145 –149,
Size of class interval of the size of class interval
two classes Lower limit of the first class = 149 – 145
= 150 – 145 class 145 – 149 = 149.5 – 144.5 = 4  (Not true)
= 5 Lower boundary of
=5 Lower limit of class 150 – 154
class 145 – 149
or
Upper boundary of
= 154 – 149 Upper limit of class 145 – 149
=5 class 145 – 149

Upper limit of class 150 – 154 Info Bulletin

The cumulative frequency of a data can also be obtained from In Example 1, class
a frequency table. The cumulative frequency of a class interval 150 – 154 is actually
is the sum of the frequency of the class and the total frequency inclusive of the values
of the classes before it. This gives an ascending cumulative from 149.5 to 154.5
frequency. because the data is a
continuous data. The
Example 2 lower boundary 149.5 and
the upper boundary 154.5
Construct a cumulative frequency table from the frequency table are used to separate the
below. classes so that there are
no gaps between 149 cm
Age 10 – 19 20 – 29 30 – 39 40 – 49 50 – 59 and 150 cm, also 154 cm
and 155 cm.

Frequency 4 5 8 7 3

Solution: Frequency Cumulative frequency Info Bulletin
Age

10 – 19 4 4 • Continuous data is

20 – 29 5+ 9 This value of a data measured on
17 means there a continuous scale.

30 – 39 8+ 17 are 17 people For example, the time
aged 39 years taken by pupils to buy
7+
40 – 49 24 old and below food at the canteen,

50 – 59 3+ 27 and the pupils’ heights.
• Discrete data is a data

CHAPTER 7 involving counting.

Histogram For example, the
number of pupils in
Mathematics Club.

Histogram is a graphical representation in which the data is

grouped into ranges by using contiguous bars. The height of the

bar in histogram represents the frequency of a class. Steps for constructing a histogram:

Find the lower Choose an appropriate scale on the Draw bars that represent each
boundary and upper vertical axis. Represent the frequencies class where the width is equal to
boundary of each on the vertical axis and the class the size of the class and the height
class interval. boundaries on the horizontal axis. is proportionate to the frequency.

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CHAPTER 7 Measures of Dispersion for Grouped Data

Frequency polygon Info Bulletin

A frequency polygon is a graph that displays a grouped data Histogram and frequency
by using straight lines that connect midpoints of the classes polygon can only be
which lie at the upper end of each bar in a histogram. Steps for constructed by using
constructing a frequency polygon: continuous data.

Mark the midpoints Mark the midpoints before the Draw straight lines
of each class on top first class and after the last by connecting the
of each bar. class with zero frequency. adjacent midpoints.

Example 3

The frequency table below shows the speed of cars in km h–1, recorded by a speed trap camera
along a highway in a certain duration. Represent the data with a histogram and frequency
polygon by using a scale of 2 cm to 10 km h–1 on the horizontal axis and 2 cm to 10 cars on
the vertical axis.

Speed (km h–1) 70 – 79 80 – 89 90 – 99 100 – 109 110 – 119 120 – 129
Number of cars 5 10 20 30 25 10

Solution: Number Midpoint Lower Upper By using the frequency
of cars boundary boundary polygon, explain the
Speed 74.5 speed of cars of more
(km h–1) 5 84.5 69.5 79.5 than 90 km h–1.
70 – 79 10 94.5 79.5 89.5
80 – 89 20 104.5 89.5 99.5
90 – 99 30 114.5 99.5 109.5
100 – 109 25 124.5 109.5 119.5
110 – 119 10 119.5 129.5
120 – 129

Histogram: Frequency polygon:

Speeds of Cars
Midpoint

30

20

10

0
69.5 79.5 89.5 99.5 109.5 119.5 129.5
Speed (km h–1)

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Number of cars Speeds of Cars
Number of cars

CHAPTER 7
30
20
10
0

69.5 79.5 89.5 99.5 109.5 119.5 129.5
Speed (km h–1)

The frequency polygon can also be constructed without constructing a histogram. Steps for
constructing a frequency polygon from a frequency table:

Add one class Find the Choose an appropriate scale Mark the Connect
interval before the midpoint on the vertical axis. Represent midpoint each
first class and after of each the frequencies on the vertical with the midpoint
the last class with class axis and the midpoints on corresponding with a
zero frequency. interval. the horizontal axis. frequency. straight line.

Example 4

The frequency table below shows the time in seconds, recorded by 20 participants in a qualifying
round of a swimming competition. Represent the data with a frequency polygon by using a scale
of 2 cm to 5 seconds on the horizontal axis and 2 cm to 2 participants on the vertical axis.

Time recorded (s) 50 – 54 55 – 59 60 – 64 65 – 69 70 – 74
Number of participants 2 3 6 5 4

Solution:

Time Number of Midpoint Time Recorded of Participants
recorded participants 6
CHAPTER 7
Number of participants(s)0 474
45 – 49 2 52
50 – 54 3 57 2
55 – 59 6 62
60 – 64 5 67 0
65 – 69 4 72 47 52 57 62 67 72 77
70 – 74 0 77 Time (s)
75 – 79
Add a class interval with zero frequency before the
first class and after the last class

Self Practice 7.1a

1. The data below shows the time taken by 50 pupils to go to school from their houses.
The time recorded is in the nearest minute.

6 15 32 16 18 31 38 20 17 32
18 8 25 35 13 24 14 8 8 25
16 25 30 10 18 14 14 10 25 30
23 30 12 18 6 23 1 15 30 12
40 15 5 14 22 49 12 19 33 25

Construct a frequency table such that there are 5 classes. Then, state the lower limit, upper
limit, midpoint, lower boundary and upper boundary of each class interval.

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CHAPTER 7 Measures of Dispersion for Grouped Data

2. The frequency table below shows the masses in kg, of new-born babies in a hospital in
a month. State the midpoint, lower limit, upper limit, lower boundary, upper boundary
and cumulative frequency of the data.

Mass (kg) 2.0 – 2.4 2.5 – 2.9 3.0 – 3.4 3.5 – 3.9 4.0 – 4.4

Number of babies 9 15 24 20 10

3. The frequency table below shows the number of hours of sleep per day of a group of
workers in a factory. By using a scale of 2 cm to 1 hour on the horizontal axis and
2 cm to 20 workers on the vertical axis, construct a histogram and frequency polygon
on the same graph to represent the data.

Number of
hours of 4.05 – 5.04 5.05 – 6.04 6.05 – 7.04 7.05 – 8.04 8.05 – 9.04 9.05 – 10.04 10.05 – 11.04
sleep per day

Number of 2 4 22 64 90 14 2
workers

4. The frequency table below shows the height in m, of sugar cane plants or also known
as Saccharum officinarum taken from a plantation. Represent the data with a frequency
polygon by using a scale of 2 cm to 1 m on the horizontal axis and 2 cm to 10 sugar
cane plants on the vertical axis.

Height (m) 1.0 – 1.9 2.0 – 2.9 3.0 – 3.9 4.0 – 4.9 5.0 – 5.9 6.0 – 6.9

Number of sugar cane plants 25 33 46 50 44 36

How to compare and interpret the dispersions based on
histogram and frequency polygon?

Distribution shapes of data Compare and interpret
the dispersions of two
When describing a grouped data, it is important to be able to or more sets of grouped
recognise the shapes of the distribution. The distribution shapes data based on histogram
can be identified through a histogram or frequency polygon. and frequency polygon,
hence make conclusion.

MIND MOBILISATION 2 Group

Aim: To explore the possible shapes of a distribution. CHAPTER 7

Steps: Scan the QR
1. Divide the class into groups. code or visit
2. Open the worksheet by scanning the QR code. Each group is bit.do/WSChap7ii
to obtain the
given the worksheet. worksheet.
3. In the group, classify the distribution shapes into two categories,

symmetrical or skewed.

Discussion:
Can you differentiate between symmetrical and skewed shapes?

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The results of Mind Mobilisation 2 show that a distribution Info Bulletin
is symmetric if the shape and size of the distribution are
almost the same when divided into two parts, left and Other distribution shapes:
right. The shape of distribution is skewed if one tail of the (i) U-shaped
histogram is longer than the other tail.
Frequency
Symmetric Histogram

Frequency Frequency Variable
(ii) J-shaped

0 0 Variable Frequency
Variable Uniform-shaped
Variable
Bell-shaped (iii) Reverse J-shaped

Skewed Histogram Frequency

Frequency Frequency Variable
(iv) Bimodal

0 0 Variable Frequency
Variable Left-skewed

Right-skewed

Variable

Example 5

The diagram below shows two histograms representing the time taken by 25 swimmers to
complete two different events.

100 m Backstroke 100 m Freestyle

CHAPTER 7 66 Number of swimmers
Number of swimmers
44

22

0 69.5 74.5 79.5 84.5 89.5 94.5 99.5 104.5 0 69.5 74.5 79.5 84.5 89.5 94.5 99.5 104.5
Time (s) Time (s)
 

(a) State the distribution shape of the histogram for the two Distributions are most
events. often not perfectly
shaped. Therefore, it is
(b) Which event has a wider dispersion of the time taken? necessary to identify an
Give your reason. overall pattern.

(c) Between backstroke and freestyle, in which event did the
swimmers perform better?

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CHAPTER 7 Measures of Dispersion for Grouped Data

Solution: FrequencyTo determine distribution
shape using hands:
(a) The histogram for the 100 m backstroke shows a bell- (i) Skew to the right
shaped distribution and for 100 m freestyle shows a
uniform distribution. Variable
(ii) Skew to the left
(b) The 100 m backstroke event has a wider dispersion
because the difference of the time recorded is larger, that
is 30 seconds (102 s – 72 s).

(c) 100 m freestyle. This is because most of the swimmers
recorded a better time.

Example 6 Frequency

The frequency polygon below shows the selling prices of the Variable
houses that were sold in two different areas in the last six months.
Area A
Selling Prices of Houses in Area A and Area B Area B

House units 20
18
16
14
12
10
8
6
4
2
0
64 999.5
99 999.5
134 999.5
169 999.5
204 999.5
239 999.5
274 999.5
309 999.5
344 999.5
379 999.5

Selling prices (RM) CHAPTER 7

(a) State the distribution shapes in the two areas.
(b) Compare the dispersions of the house prices in the two areas.
(c) In your opinion, which area represents an urban area and which area represents a rural

area?
Solution:

(a) The distribution shape of the selling prices in area A is skewed to the right whereas in
area B is skewed to the left.

(b) The dispersions of the selling prices in area A and area B are approximately the same
even though their distribution shapes are different.

(c) Area A represents a rural area because most of the selling prices are lower whereas
Area B represents an urban area because most of the selling prices are higher.

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Self Practice 7.1b

1. The diagram below shows two histograms of Mathematics test marks obtained by two
groups, Arif and Bestari.

Mathematics Test Marks of Arif Group Mathematics Test Marks of Bestari Group
Number of pupils Number of pupils

6 8
4 6
2 4
0 2
0 10.5 20.5 30.5 40.5 50.5 60.5 70.5 80.5 90.5
10.5 20.5 30.5 40.5 50.5 60.5 70.5 80.5 90.5
Marks Marks

(a) State the distribution shape of the histogram for the two groups.
(b) Compare the dispersions of test marks between the two groups.
(c) Which group shows better results? Give your reason.

CHAPTER 7 2. The diagram below shows the survey results of the traffic flow in two different
Number of cars locations. Each location records the speeds of 50 cars.

Speeds of Cars

22 Location A
20 Location B
18
16
14
12
10
8
6
4
2
0 0.5 20.5 40.5 60.5 80.5 100.5 120.5

Speed (km h–1)

(a) State the distribution shapes in both locations.
(b) Compare the dispersions of the car speeds in both locations.
(c) In your opinion, which location is a highway and which location is a housing area?

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CHAPTER 7 Measures of Dispersion for Grouped Data

How to construct an ogive for a set of grouped data?

Besides histogram and frequency polygon, a frequency

distribution can also be displayed by drawing a cumulative Construct an ogive for a

frequency graph, also known as an ogive. When the cumulative set of grouped data and
frequencies of a data are plotted and connected, it will produce determine the quartiles.

an S-shaped curve. Ogives are useful for determining the quartiles

and the percentiles. We will learn how to use an ogive for this purpose in the next section.

Steps for constructing an ogive:

Add one class before the first Choose an appropriate scale on Plot the Draw a
class with zero frequency. the vertical axis to represent cumulative smooth curve
Find the upper boundary the cumulative frequencies and frequency with passing
and the cumulative the horizontal axis to represent the corresponding through all
frequency for each class. the upper boundaries. upper boundary. the points.

Quartile

For a grouped data with number of data N, the quartiles can be determined from the ogive. Q1,

Q2 and Q3 are the values that correspond to the cumulative frequency N , N and 3N   respectively.
4 2 4

Example 7

The frequency table on the right Salt content Frequency • Quartiles are values that
shows the salt content of 60 types (mg) divide a set of data into
of food. 4 four equal parts. Each
(a) Construct an ogive to represent 100 – 149 11 set of data has three
150 – 199 15 quartiles, which are Q1,
the data. 200 – 249 21 Q2 (median) and Q3.
(b) From your ogive, determine 250 – 299 8
300 – 349 1 • The first quartile Q1,
(i) the first quartile 350 − 399 also known as the lower
(ii) the median quartile, is the middle
(iii) the third quartile value of the lower half
of the data before the
Solution:
median or a quartile that
(a) Salt content Frequency Upper Cumulative contains 25% of the data.
(mg) boundary frequency
• The second quartile, Q2, CHAPTER 7
50 – 99 0 99.5 0 also known as median
100 – 149 4 149.5 4 is the middle value of a
150 – 199 11 199.5 15 set of data.
200 – 249 15 249.5 30
250 – 299 21 299.5 51 • The third quartile, Q3,
300 – 349 8 349.5 59 also known as the upper
350 − 399 1 399.5 60 quartile, is the middle
value of the upper half
of the data after the
median or a quartile
that contains 75% of the
data.

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Salt Content in Foods Steps to determine the quartiles:
Cumulative frequency
1. Number of data, N = 60, therefore N = 15,
60 4
N 3N
50 2 = 30 and 4 = 45.
45
40 2. Draw a horizontal line from the axis of

30 cumulative frequency at 15 until it intersects

20 the ogive.
15
10 3. From the intersection point in step 2, draw

284.5 the vertical line down until it meets the axis

0 of salt content at the horizontal axis.
99.5 149.5 199.5 249.5 299.5 349.5 399.5
Salt content (mg) 4. The value of the salt content obtained is the

value of Q1.
5. Repeat steps 2 to 4 for the values of 30 and

45 to obtain the values of Q2 and Q3.

(b) 1 × 60 = 15 Info Bulletin
4

From the graph, the first quartile, The salt content of 15 types The average salt
Q1 = 199.5 mg of food are less or equal to intake per day among
199.5 mg Malaysians is 7.9 g (1.6
1 × 60 = 30 teaspoons). This is above
2 The salt content of 30 types the level recommended
of food are less or equal to by the World Health
From the graph, the median, 249.5 mg Organization (WHO),
Q2 = 249.5 mg which is less than 5 g
(one teaspoon) per day.

3 × 60 = 45
4
The salt content of 45 types of food are
From the graph, the third quartile, Q3 = 284.5 mg less or equal to 284.5 mg

From Example 7, the first quartile, median and third quartile of a grouped data can be

determined by using an ogive.

Cumulative frequency The first quartile position, Q1 Ap&plicCatairoener
CHAPTER 7 1
N = 4 × total frequency, N A financial manager
—34 N needs to be an expert
—12 N The median position, Q2 in the features of market
—41 N 1 capital that involve
= 2 × total frequency, N financial assets such
0 Q1 Q2 Q3 as stocks and bonds.
Variables The third quartile position, Q3 Statistical method can
3 be used to analyse the
= 4 × total frequency, N features of market capital
through the stocks and
bonds distributions.

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CHAPTER 7 Measures of Dispersion for Grouped Data

Cumulative histogram and ogive can be constructed using cumulative frequency table.
Cumulative histogram is constructed just like histogram, but the vertical axis is represented
by cumulative frequency. By referring to Example 7, the cumulative histogram and the related
ogive are as shown below.

Salt Content in Foods Salt Content in Foods
Cumulative frequency Cumulative frequency

60 60
50 50
40 40
30 30
20 20
10 10
0 0
99.5
149.5
199.5
249.5
299.5
349.5
399.5

99.5
149.5
199.5
249.5
299.5
349.5
399.5

Salt content (mg)    Salt content (mg)

How is the construction of ogive related to the construction of cumulative histogram?

Percentile

We can analyse a large data more easily and effectively when we divide the data into
small parts which is known as percentile. A percentile is a value that divides a set of
data into 100 equal parts and is represented by P1, P2, P3, …, P99.

Example 8 Aptitude Test Score CHAPTER 7
Cumulative frequency
The ogive on the right shows the scores of an 60
aptitude test obtained from candidates who are 50
applying for a post in a company. 40
30
(a) Based on the ogive, find 20
(i) the 10th percentile, P10 10
(ii) the 46th percentile, P46 0 30.5 40.5 50.5 60.5 70.5 80.5 90.5

(b) Only those candidates who obtained 92nd Score
percentile and above will be called for an
interview. What is the minimum score required 209
in order to be called for an interview?
KPM
(c) What is the percentage of the candidates who
obtained a score of 57 and below?

Solution: Aptitude Test Score
Cumulative frequency
(a) (i) 10% of the total frequency = 10 × 50 60
100

=5

From the ogive, P10 = 46.5 50

(ii) 46% of the total frequency = 46 × 50 40
100 30

= 23 20

From the ogive, P46 = 63.5 15

10

(b) 92% of the total frequency = 92 × 50 0 77
100
30.5 40.5 50.5 60.5 70.5 80.5 90.5
46.5 Score 63.5

= 46 Info Bulletin

P92 = 77. Therefore, only candidates with a minimum 25th percentile is also
score of 77 will be called for an interview. known as first quartile,
50th percentile as median
(c) From the ogive, and 75th percentile as
third quartile.
15 × 100 = 30%
50

Therefore, 30% of the candidates obtained a score of 57 What is the difference
and below. between quartile and
percentile?
Self Practice 7.1c

CHAPTER 7 1. The frequency table on the right shows the marks Marks Number of pupils
of 100 pupils in an examination. 11 – 20 2
(a) Construct an ogive to represent the data. 21 – 30 13
(b) From your ogive, determine 31 – 40 25
(i) the first quartile 41 – 50 25
(ii) the median 51 – 60 19
(iii) the third quartile 61 – 70 10
71 – 80 4
2. The frequency table on the right shows the length 81 – 90 2
of the soles of 40 pupils.
(a) Construct an ogive to represent the data. Length of soles Number of
(b) Based on the ogive, find (cm) pupils
(i) the 20th percentile, P20
(ii) the 55th percentile, P55 21.0 – 21.9 1
(iii) the 85th percentile, P85 22.0 – 22.9 4
(c) What is the percentage of the pupils having a 23.0 – 23.9 10
sole length of 24.6 cm and below? 24.0 – 24.9 18
25.0 – 25.9 5
26.0 – 26.9 2

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CHAPTER 7 Measures of Dispersion for Grouped Data

7.2 Measures of Dispersion

How to determine range, interquartile range, variance and Determine range,
standard deviation for grouped data? interquartile range,
variance and standard
In Form 4, you have learnt ways to determine range, interquartile deviation as a measure
range, variance and standard deviation as a measure to describe to describe dispersion for
dispersion for ungrouped data. In this section, we shall proceed grouped data.
to the measures of dispersion for grouped data.

Range and Interquartile Range

Example 9

Pak Hamidi had recorded the mass of pineapples that he harvested from his farm. The

following frequency table and ogive show the data that he obtained. Determine the range and

interquartile range for the data.

Mass (g) Number of Masses of Pineapples
pineapples Cumulative frequency

80

400 – 499 6 60 Interquartile range
500 – 599 12 40 = Q3 – Q1

600 – 699 16 20

700 – 799 24 0 399.5 Interquartile range of a
800 – 899 14 499.5 set of grouped data can
900 – 999 8 599.5 be determined from ogive
699.5 by finding Q1 and Q3 first.
799.5
899.5
999.5

Mass(g)

Solution:

Range = midpoint of the highest class – midpoint of the lowest class

= 900 + 999 – 400 + 499
2 2
Difference between the Masses of Pineapples
= 949.5 – 449.5 heaviest pineapple and the Cumulative frequency CHAPTER 7
= 500 g lightest pineapple is 500 g. 80

From the ogive, the position of Q3: 60
3
the position of Q1: 4 × 80 = 60 40

14 × 80 = 20

Q1 = 614.5 Q3 = 809.5 20 Q1 = 614.5 Q3 = 809.5
0
Therefore, the interquartile Difference between the heaviest Mass (g)
range pineapple and the lightest 399.5
= 809.5 – 614.5 pineapple that lies in the middle 499.5
= 195 g 50% of the distribution is 195 g. 599.5
699.5
799.5
899.5
999.5

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Variance and Standard Deviation

Variance and standard deviation for a grouped data can be • Variance is the average
obtained using the following formulae. of the square of the
difference between each
Variance, σ2 Standard deviation, σ where data and the mean.
x = midpoint of the
= ∑  f x2 – –x 2 = ∑  f x2 – –x 2 class interval • Standard deviation is a
∑  f ∑  f f = frequency measure of dispersion
–x = mean of the data relative to its mean,
which is measured in
Example 10 the same unit of the
original data.

The frequency table below shows the volumes of water to the nearest litres, used daily by a
group of families in a housing area. Calculate the variance and standard deviation of the data.

Volume of water (l) 150 – 159 160 – 169 170 – 179 180 – 189 190 – 199 200 – 209

Number of families 8 12 15 24 20 16

Solution:

Volume of Frequency, Midpoint, fx x2 fx2
water (l) f x
150 – 159 8 1 236 23 870.25 190 962
160 – 169 12 154.5 324 723
170 – 179 164.5 1 974 27 060.25 456 753.75
15 816 966
180 – 189 174.5 2 617.5 30 450.25 756 605
190 – 199 24 669 124
200 – 209 20 184.5 4 428 34 040.25 ∑  fx2 = 3 215 133.75
16 194.5
∑  f = 95 204.5 3 890 37 830.25

3 272 41 820.25

∑  fx = 17 417.5

Mean, –x = ∑  fx ChAecnkswinegr
∑ f

= 17 417.5
95
= 183.34 l 1. Press MODE MODE

CHAPTER 7 Variance, σ2 = ∑  fx2 – –x 2 Display SD Reg Base
∑  f Choose 1 1 2 3

1 2 2. ESnHteIFr T(mid,po(ifnret)q, upernecsys)
= 3 215 133.75 – 17 417.5 2 M+  , and repeat for the
95 95 subsequent values.

= 229.1856

= 229.19 l2 (correct to 2 decimal places) 3 . PDrisepslsayA C–x SHIFT 2
xσn xσn–1
∑  fx2 – –x 2
Standard deviation, σ = ∑  f 1 2 3

= 229.1855956 Press 1 for mean:
Display 183.3421053
= 15.1389 Press 2 for standard deviation:
Display 15.13887696
= 15.14 l (correct to 2 decimal places)

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CHAPTER 7 Measures of Dispersion for Grouped Data

Self Practice 7.2a

1. The frequency table below shows the electricity bills of apartment units for a certain
month.

Electricity bill (RM) 30 – 49 50 – 69 70 – 89 90 – 109 110 – 129

Number of apartment units 4 9 11 15 13

Construct an ogive for the data and hence, calculate the range and interquartile range.
Explain the meaning of the range and interquartile range obtained.

2. Calculate the variance and standard deviation of each of the following data. Give your
answer correct to two decimal places.

(a) Time (minutes) 1 – 2 3 – 4 5 – 6 7 – 8 9 – 10 11 – 12

Frequency 15 20 28 35 30 24

(b) Distance (m) 11 – 20 21 – 30 31 – 40 41 – 50 51 – 60 61 – 70 71 – 80

Frequency 5 8 13 20 22 21 11

How to construct and interpret a box plot for a set of

grouped data? Construct and interpret

You have learnt that a box plot is a method to display a a box plot for a set of
group of numerical data graphically based on the five number grouped data.

summary of data. They are the minimum value, first quartile,

median, third quartile and maximum value. Similar to the histrogram and frequency polygon,

the shape of a distribution can also be identified through the box plot.

(a) (b)(i) (b)(ii)

Whisker Whisker

Q1 Q2 Q3 Q1 Q2 Q3    Q1 Q2 Q3
Symmetric distribution
Left-skewed distribution Right-skewed distribution

(a) The median lies in the middle of the box and the whiskers are about the same CHAPTER 7
length on both sides of the box.

(b) The median cuts the box into two different sizes.
(i) If the left side of the box is longer, then the data distribution is left-skewed.
(ii) If the right side of the box is longer, then the data distribution is right-skewed.

Left whisker and right whisker represent the score outside of the median. If the box is
divided into the same size but the left whisker is longer than the right whisker, then the
data distribution is left-skewed, and vice versa.

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Example 11 Masses of Starfruits Info Bulletin

The ogive on the right shows 90 Ogive and box plot on the
the masses in g, of same graph:
90 starfruits. Cumulative frequency 80
(a) Construct a box plot 70 Position of Q3 Masses of Starfruits

based on the ogive. 60 90
(b) Hence, state the
50 Position of Q2 Cumulative frequency 80
distribution shape of the 40
data. 70

Solution: 30 Position of Q1 60
(a) From the ogive: 20
50

10 Minimum 123 Maximum 40
0
116 128 30

•  Minimum value = 80 80 20
• Maximum value = 150 90
100 10 116 123 128
110 0
120
130
140
150
Mass (g)
80
1 90
4 100
110
120
130
140
150
Mass (g)
•  Position of Q1: × 90 = 22.5

Q1 = 116 Info Bulletin

1
• Position of Q2: 2 × 90 = 45 25% 25% 25% 25% of data

Q2 = 123

3
• Position of Q3: 4 × 90 = 67.5

Q3 = 128

Box plot:

80 90 100 110 120 130 140 150

Mass (g)

(b) The distribution of the data is skewed to the left because the left side of the box plot is

longer than the right side of the box plot.

Self Practice 7.2b Units of Power Consumed
1. The ogive on the right shows the number of units
80
of electrical power, consumed by 80 households in 70
a particular month. 60
(a) Construct a box plot based on the ogive. 50
(b) Hence, state the distribution shape of the data. 40
30
214 20
10
KPM 0
CHAPTER 7
Cumulative frequencyElectrical power (units)
50
100
150
200
250
300
350
400
450

2. The ogive on the right shows the Cumulative frequency CHAPTER 7 Measures of Dispersion for Grouped Data
duration in seconds, of 60 songs
aired by a radio station at a certain Duration of Songs
time. 60
(a) Construct a box plot based on
the ogive. 40
(b) Hence, state the distribution
shape of the data. 20

0
149.5 199.5 249.5 299.5 349.5 399.5 449.5
Duration (s)

How to compare and interpret two or more sets of Compare and interpret
grouped data based on measures of dispersion? two or more sets of
grouped data, based on
Example 12 measures of dispersion
hence make conclusion.
A botanist sowed 40 samples of hibiscus seeds using two
different hybrids, A and B. The diameters of both hybrids are
measured under close guard to develop an extra-large hibiscus.
The following frequency table shows the diameters of petals for
hybrid A and B.

Diameter (cm) 13.0 – 13.4 13.5 – 13.9 14.0 – 14.4 14.5 – 14.9 15.0 – 15.4
Hybrid A 4 8 9 10 9
Hybrid B 9 10 8 6 7

Based on the mean and standard deviation, determine which hybrid produces larger and more
consistent petals. Justify your answer.

Solution:
For hibiscus of hybrid A,

Diameter Frequency, Midpoint, fx x2 fx2 CHAPTER 7
(cm) f x
4 52.8 174.24 696.96
13.0 – 13.4 8 13.2 109.6 187.69 1 501.52
13.5 – 13.9 9 13.7 127.8 201.64 1 814.76
14.0 – 14.4 10 14.2 147 216.09 2 160.9
14.5 – 14.9 9 14.7 136.8 231.04 2 079.36
15.0 – 15.4 15.2 ∑ fx = 574 ∑ fx2 = 8 253.5
∑ f = 40

Mean, –x = 574 Standard deviation, σ = 8 253.5 – 14.352
40 40

= 14.35 cm = 0.415

= 0.64 cm

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For hibiscus of hybrid B,

Diameter Frequency, Midpoint, fx x2 fx2
(cm) f x
9 118.8 174.24 1 568.16
13.0 – 13.4 10 13.2 137 187.69 1 876.9
13.5 – 13.9 8 13.7 113.6 201.64 1 613.12
14.0 – 14.4 6 14.2 88.2 216.09 1 296.54
14.5 – 14.9 7 14.7 106.4 231.04 1 617.28
15.0 – 15.4 15.2 ∑ fx = 564 ∑ fx2 = 7 972
∑ f = 40

Mean, –x Standard deviation, σ

= 564 = 7 972 – 14.12
40 40

= 14.1 cm = 0.49

= 0.7 cm Tunku Abdul Rahman
Putra Al-Haj declared
Hybrid A produces larger petals because the mean is larger the hibiscus as The
than hybrid B (14.35 cm . 14.1 cm) and the smaller standard National Flower in 1960.
deviation (0.64 cm , 0.7 cm) shows that the diameter of the The five petals of the
petals is more consistent. flower represent the
five principles of Rukun
Negara.

Self Practice 7.2c

1. A ball manufacturing factory needs to regulate the internal air pressure in psi, of the
produced ball before being marketed. The frequency table below shows the internal air
pressures of 50 ball samples taken from machine P and machine Q.

Air pressure 8.0 – 8.9 9.0 – 9.9 10.0 – 10.9 11.0 – 11.9 12.0 – 12.9 13.0 – 13.9
(psi)

Machine P 7 11 13 12 5 2

Machine Q 1 3 5 20 18 3

CHAPTER 7 The factory specified that the internal air pressure of a ball should be between 11.3 psi to
11.7 psi. Which machine shows better performance in terms of air pressure accuracy?

2. The frequency table below shows the lifespans in years, of brand X and brand Y batteries.

Lifespan (years) 0 – 0.9 1.0 – 1.9 2.0 – 2.9 3.0 – 3.9 4.0 – 4.9
Brand X battery 4 10 17 20 9
Brand Y battery 10 21 15 8 6

By using suitable measures, determine which brand of battery is better and lasts longer.

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CHAPTER 7 Measures of Dispersion for Grouped Data

How to solve problems involving measures of dispersion Solve problems involving
for grouped data? measures of dispersion
for grouped data.
Example 13

A survey on the duration of time in Cumulative frequency Time Spent by Customers
hours, spent by customers to buy goods 80
in a supermarket is carried out. The
results of the survey are shown in the 60
ogive on the right.
40
(a) Construct a frequency table for the
time taken by the customers to buy 20
goods in the supermarket using
the classes 0.5 – 0.9, 1.0 – 1.4, 0
1.5 – 1.9, 2.0 – 2.4 and 2.5 – 2.9. 0.45 0.95 1.45 1.95 2.45 2.95
Time (hours)
(b) Hence, estimate the mean and
standard deviation of the data.

Solution:

Understanding the problem Devising a strategy

Determine the mean and standard (a) Construct the frequency table from the ogive.
deviation from the ogive. (b) Calculate the mean and standard deviation

using formula.

Implementing the strategy Time Spent by Customers

(a) 80

Time Number of 6–0=6 Cumulative frequency 70 CHAPTER 7
(hours) customers 22 – 6 = 16
0.5 – 0.9 54 – 22 = 32 60
1.0 – 1.4 6 70 – 54 = 16
1.5 – 1.9 16 80 – 70 = 10 54
2.0 – 2.4 32
2.5 – 2.9 16 40
10
22

20

6

0
0.45 0.95 1.45 1.95 2.45 2.95
Time (hours)

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(b) Time Frequency, Midpoint, fx x2 fx2
(hours) f x
0.5 – 0.9 6 0.7 4.2 0.49 2.94
1.0 – 1.4 16 1.2 19.2 1.44 23.04
1.5 – 1.9 32 1.7 54.4 2.89 92.48
2.0 – 2.4 16 2.2 35.2 4.84 77.44
2.5 – 2.9 10 2.7 27 7.29 72.9
∑ fx = 140 ∑ fx2 = 268.8
∑ f = 80

Mean, –x = 140 Standard deviation, σ = 268.8 – 1.752
80 80

= 1.75 hours = 0.2975

= 0.55 hours

Making a conclusion Number of customers (b) Mean, –x = 1.75 hours
6 Standard deviation, σ = 0.55 hours
(a) Time (hours) 16
0.5 – 0.9 32
1.0 – 1.4 16
1.5 – 1.9 10
2.0 – 2.4
2.5 – 2.9

Self Practice 7.2d

1. The histogram on the right shows the Blood Glucose Readings

blood glucose readings taken from a 40
group of patients in a clinic.
CHAPTER 7
Frequency
(a) Based on the histogram, is the 30

distribution symmetrical? Give your 20

reason.

(b) Calculate the mean and standard 10
deviation of the blood glucose

readings. 0
(c) Compare the standard deviation of 2.95 3.95 4.95 5.95 6.95 7.95 8.95
Glucose level (mmol/L)
the blood glucose readings between

6.0 mmol/L and 8.9 mmol/L with

the standard deviation in (b). Justify your answer.

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CHAPTER 7 Measures of Dispersion for Grouped Data

2. The table below shows the results of statistical analysis for the price in RM, of 10 kg
of rice in supermarket P and supermarket Q. The number of data taken is 20 rice bags
from each supermarkets respectively.

Supermarket Mean Standard Minimum First Median Third Maximum
deviation value quartile quartile value
P 32 32
Q 32 5.62 26 30 34 34 40

4.05 26 32 34 40

(a) State the mean and range of the price of the rice in both supermarkets.
(b) The price distribution of the rice in which market is more symmetric? Explain your

answer.
(c) Discuss about the median and interquartile range of the two data.

How to design and conduct a mini-project involving Design and conduct a
statistical investigations? mini-project involving
statistical investigations
ProjeCT based on measures of
central tendency and
The statistical data collected by the National Health and measures of dispersion
Morbidity Survey (NHMS) shows that more Malaysians are and hence interpret and
becoming obese with the rate of one in two adults suffering communicate research
from overweight. Other surveys also found that overweight and findings.
obesity among school pupils make up 30% of the population.
Obesity increases the chances of developing health problems
such as diabetes, heart disease and stroke.

Your school has decided to launch “Activate Your Life” campaign with the aim to create
awareness among pupils about obesity and motivate them to adopt healthy lifestyle. Your
mathematics teacher wishes to display the health level of pupils on the school bulletin
board according to their gender.

Title: Health Level of Pupils CHAPTER 7

Material: Measuring tape, weighing scale You can carry out the
research outside the
Procedure: teaching and learning
1. Each group will investigate the health level of (PdP) session.

pupils based on their gender by using the Body
Mass Index (BMI). Divide the class into five
groups where each group conducts survey to Form
1, 2, 3, 4 and 5 pupils. Fix the equal number of
respondents according to gender from each form.

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2. Each group is asked to prepare a project report as part of the learning in the class.

The report needs to cover the following aspects:

(a) Survey

Generate suitable questions such as gender, height, mass and the number of

hours spent in sport activities by the respondents within a week as part of the

data collection process.

(b) Data collection method

Choose a collection method to obtain the data.

Choose your respondents randomly. You can organise the

(c) Data organisation method data and construct the
Construct a frequency table to organise your data. graphical representation
using electronic
Choose an appropriate class interval for each data. spreadsheet.
(d) Graphical representations

Present your data using histogram, frequency

polygon and other suitable representations.

(e) Data analysis

(i) Calculate the suitable measures of central tendency and measures of

dispersion for each of your data.

(ii) Calculate the Body Mass Index (BMI) of each pupil using the following

formula. Mass (kg)
(m) × Height
BMI = Height (m)

(iii) The table below shows the BMI according to age for a teenage boy.

Age Underweight Normal Overweight Obese

13 < 14.8 14.9 – 20.8 20.9 – 24.8 . 24.8

14 < 15.4 15.5 – 21.8 21.9 – 25.9 . 25.9

15 < 15.9 16.0 – 22.7 22.8 – 27.0 . 27.0

16 < 16.4 16.5 – 23.5 23.6 – 27.9 . 27.9

17 < 16.8 16.9 – 24.3 24.4 – 28.6 . 28.6

The table below shows the BMI according to age for a teenage girl.

Age Underweight Normal Overweight Obese
21.9 – 26.2 . 26.2
13 < 14.8 14.9 – 21.8 22.8 – 27.3 . 27.3
22.6 – 28.2 . 28.2
CHAPTER 7 14 < 15.3 15.4 – 22.7 24.2 – 28.9 . 28.9
24.9 – 29.3 . 29.3
15 < 15.8 15.9 – 22.5

16 < 16.1 16.2 – 24.1

17 < 16.3 16.4 – 24.8

Source: World Health Organization (WHO), 2007

Based on the BMI table and the data collected, determine the percentage
of pupils that are under the category ‘Underweight’ and ‘Obese’ by
constructing an ogive.

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CHAPTER 7 Measures of Dispersion for Grouped Data

(f) Description and conclusion
(i) Interpret your findings of the research. Make conclusions about the
physical state of pupils according to their gender for each form.
(ii) Suggest follow-up actions that need to be taken by the pupils who are
underweight, overweight and obese.

3. Write down your findings of the research on the cardboards and paste it on your
school bulletin board.

Summary Arena

MEASURES OF DISPERSION FOR GROUPED DATA

Data Representation

Histogram and frequency Ogive: Box plot:
polygon:
Cumulative frequency Mass (kg)
Frequency 50
20 40
15 30
10 20
5 10

0 0

Mass (kg) Mass (kg)
9.5
14.5
19.5
24.5
29.5
34.5
9.5
14.5
19.5
24.5
29.5
34.5

9.5
14.5
19.5
24.5
29.5
34.5
CHAPTER 7
Measures of Dispersion

Range Interquartile range Variance, σ2 = ∑  fx2 – –x 2
= Midpoint of Midpoint of = Q3 – Q1 ∑  f
the highest – the lowest (The values of Q3 and
class class Q1 are determined
from ogive)
Standard deviation, σ
Percentile
= ∑  fx2 – –x 2
∑  f

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Reflection

At the end of this chapter, I can

construct histogram and frequency polygon for a set of grouped data.

compare and interpret the dispersions of two or more sets of grouped data based
on histogram and frequency polygon, hence make conclusion.
construct an ogive for a set of grouped data and determine the quartiles.

determine range, interquartile range, variance and standard deviation as a
measure to describe dispersion for grouped data
construct and interpret a box plot for a set of grouped data.

compare and interpret two or more sets of grouped data, based on measures of
dispersion hence make conclusion.
solve problems involving measures of dispersion for grouped data.

design and conduct a mini-project involving statistical investigations based on
measures of central tendency and measures of dispersion and hence interpret
and communicate research findings.

MINI PROJECT

You are required to investigate the population distribution

of Malaysia, Indonesia and Singapore from 1990 to 2019.

You can obtain the population data by scanning the QR

code on the right.

Then, organise the data in frequency table using Scan the QR code or
the appropriate class interval. Construct a suitable data visit bit.do/MPChap7 to
representation to see the data distribution. obtain the population

For the data of each country, obtain the values of the data.

measures of central tendency and the measures of dispersion.

By using the value of suitable measure, compare the populations in these three countries

from the aspect of total population and population dispersion. Make a conclusion for the

population distribution and relate it with the population density in each country.

CHAPTER 7 Extensive Practice Scan the QR code or visit
bit.do/QuizE07 for interactive quiz

UNDERSTAND

1. For each of the following class intervals, determine the lower limit, upper limit, midpoint,
lower boundary and upper boundary.

(a) Length (m) 10 – 14 15 – 19 20 – 24 25 – 29 30 – 34

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CHAPTER 7 Measures of Dispersion for Grouped Data

(b) Volume (cm3) 25.0 – 25.9 26.0 – 26.9 27.0 – 27.9 28.0 – 28.9 29.0 – 29.9

(c) Mass (g) 0 – 0.24 0.25 – 0.49 0.50 – 0.74 0.75 – 0.99

2. Identify whether the following descriptions is for a histogram, a frequency polygon or
an ogive.
(a) Graph that represents cumulative frequency of classes in a
frequency distribution.

(b) Displays data using side by side bars. The height of the bar is
used to represent the class frequency.

(c) Displays data using straight lines that connect the midpoints
of the class interval. Frequency is represented by the height of
these midpoints.

3. The box plot below shows the distribution shapes of data. Match the following histograms
with the corresponding box plot in the space provided.

A B C D
(a) Frequency (b) Frequency (c) Frequency (d) Frequency

Variable Variable Variable Variable

MASTERY

4. The data on the right shows the heights in cm, of 30 pupils in 146 163 156 CHAPTER 7
Form 5. 152 174 156
(a) Organise the data by completing the frequency table below. 178 151 148
Then, draw a histogram of the data using a suitable scale. 166 154 150
164 157 171
Height Lower Upper Tally Frequency 168 159 170
(cm) boundary boundary 163 157 161
167 162 157
145 − 149 166 160 155
168 158 162
150 – 154
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(b) Construct a new frequency table by rearranging the class intervals beginning with
145 – 148 cm, 149 – 152 cm, 153 – 156 cm and so forth. Hence, construct a
histogram to display the data.

(c) Compare the distribution shapes of the two histograms. In your opinion, what is the
conclusion that can be made from this comparison?

5. The frequency table below shows the time spent watching television in a week by
30 families.

Time (hours) 2 – 4 5 – 7 8 – 10 11 – 13 14 – 16 17 – 19 20 – 22

Number of 8 9 6 4 2 0 1
families

(a) On the same graph, construct a histogram and frequency polygon of the data using
a suitable scale.

(b) Comment on the distribution shape of the data displayed.

6. The frequency table below shows the Mathematics test marks of a group of pupils.

Marks 40 – 49 50 – 59 60 – 69 70 – 79 80 – 89 90 – 99

Number of pupils 4 8 12 10 9 7

Draw an ogive of the data and calculate
(a) the range,
(b) the interquartile range,
(c) the 40th percentile and 80th percentile for the test marks.

CHALLENGE

7. Khuzairi is a dairy cow raiser. He rears 130 dairy cows in his farm. The frequency table
below shows the volumes in litres, of milk produced by his cows in a certain week.

Volume of milk (litres) 5 – 10 11 – 16 17 – 22 23 – 28 29 – 34 35 – 40
Number of dairy cows
15 28 37 26 18 6

(a) Construct a cumulative histogram of the data.
(b) On the same graph in (a), construct an ogive. Hence, estimate the interquartile

range of the distribution.

CHAPTER 7 8. The frequency table below shows the blood pressure readings taken from a group of patients
before and after taking a dose of a type of medicine in lowering blood pressure.

Systolic blood pressure (mmHg) 120 − 134 135 − 149 150 − 164 165 − 179
Before 4786
After 9871

Calculate the mean and standard deviation of the data. Is the medicine effective in
lowering down the blood pressure of the group of patients after taking a dose of the
medicine? Justify your answer.

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CHAPTER 7 Measures of Dispersion for Grouped Data

9. The ogive on the right shows the distances of Distances of Shot-put Throws
shot-put throws obtained by Rozaidy and Wildan
in a training session. 20
(a) Calculate the percentage of the throwing Cumulative frequencyRozaidy
distances that exceeds 15.45 m obtained by 10.45Wildan
Rozaidy and Wildan. 12.45
(b) Based on the median and the third quartile 14.4515
of both performances, determine who 16.45
perform better during the training session. 18.4510
20.45
5

0

Cumulative frequency Distance (m)

10. Volumes of petrol consumed by 100 cars were recorded. The ogive shows the volume
of petrol consumed for a 60-km journey and the box plot shows the volume of petrol
consumed for a 100-km journey.

Volume of Petrol for 60-km Journey

100
Volume of Petrol for 100-km Journey

80

60

40 4.45 4.95 5.45 5.95
Volume of petrol (litres)

20  

0 2.45 2.95 3.45 3.95 4.45 4.95 5.45 5.95
Volume of petrol (litres)

(a) Redraw the ogive for the 60-km journey. On the same graph, draw an ogive for the
volume of petrol consumed for the 100-km journey.

(b) If a car uses 3.7 litres petrol for the 60-km journey, calculate the volume of petrol
consumed for the 100-km journey. Justify your answer.

EXPLORING MATHEMATICS CHAPTER 7
Instructions:
(i) Do this activity in a small group. Scan the QR
(ii) Each group answer the question in the activity worksheet code or visit
bit.do/EMChap7 to
(scan the QR code). perform this activity.
(iii) After completing the worksheet, each group needs to

construct a mind map that summarises the distribution
shape and the suitable measures to describe the data.
(iv) Present the outcome of your group. The best presentation
will be displayed at the Mathematics corner in your class.

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8CHAPTER Mathematical Modeling

What will you learn?
• Mathematical Modeling

Why study this chapter?
Mathematical modeling is used in various disciplines in the real world. Engineers use
mathematical modeling to analyse the traffic flow on a bridge. Telecommunication
companies use mathematical modeling to determine the charges for the calls that
consumers make. Scientists also use mathematical modeling to predict the trends in
population growth and the spread of infectious diseases to ensure the well-being of
human race.

Do you know?

The Covid-19 pandemic has hit the world in 2019. In
this regard, the Malaysian government implemented the
Movement Control Order (MCO) in an effort to flatten the
epidemiological curve of Covid-19 cases in our country.
Mathematical modeling can be used to make epidemic
predictions.

For more information:

  bit.do/DoYouKnowChap8

WORD BANK

CHAPTER 8 exponent eksponen
exponential function fungsi eksponen
quadratic kuadratik
linear linear
mathematical modeling pemodelan matematik

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The construction of the SMART (Stormwater Management and Road Tunnel)

tunnel aims to drain flood water during heavy rain in Kuala Lumpur. However, the
tunnel also has an additional function in reducing traffic congestion. The unique
design and innovative way of operating the tunnel presented challenges to the
engineers at the beginning of its construction. Do you know that mathematical
modeling was used to demonstrate the four different operation modes of the
SMART tunnel?

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8.1 Mathematical Modeling Explain mathematical
modeling.
What is mathematical modeling?

The world around us is filled with various important questions
that are not answered. For example,

What is the effect of rising sea levels on the coastal
regions of Malaysia?

How much will it cost to go to college or university in
10 years?

Will the population in Malaysia surpass 40 million?

CHAPTER 8 Is it possible to identify the personality trait of cybercrime
victims by studying the behaviours of the web surfers?

Answers to these questions are constantly being studied by researchers. Will they be able to
find the answers? Maybe. The only thing one can say with certainty is that any attempt to
find the solution requires the use of mathematics, most likely through the creation, application
and refinement of mathematical models.
A mathematical model is a mathematical relation that describes the real-world situation.
For example, the formula I = Prt is a relation between simple interest and the other three
quantities, that is, the principal, the interest rate and the time.
In this chapter, you will be introduced to the process of constructing mathematical
models, which is called mathematical modeling. In mathematical modeling, a real-world
problem will be translated into a mathematical problem. We then solve the mathematical
problem and interpret its solution in terms of the real-world problem.

A mathematical model is a representation of a system or scenario that is used to gain
qualitative and/or quantitative understanding of some real-world problems and to predict
future behaviour.

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CHAPTER 8 Mathematical Modeling CHAPTER 8

Consider the following problems.

1 The population of town A is 40 000. It is known that 45% of the residents in the

town practise the habit of recycling used plastic drinking bottles. If each person in
the town uses 5 plastic drinking bottles per week, how many bottles are recycled each
week in the town?

This type of question is often asked in Mathematics books to reinforce the concept of
percentage. This is an example of a problem solving question. The problem explicitly gives
us all the information we need. We only need to determine the appropriate computations to
arrive at one correct answer. This kind of problem solving question can be used to help us
understand a particular mathematical concept and reinforce important mathematical skills.

Let us look at the following question.

2 How long does it take to clean up an oil spill in the ocean?

The second question is quite different. We do not have enough information to answer
this question. It is an open-ended question. We usually do not have complete information
when trying to solve real-world problems. These real-world problems demand us to use both
mathematics knowledge and creativity to solve them. In this case, mathematical modeling is
perfect for solving such open-ended questions.

There are a few important components in mathematical modeling:

1 Identifying and defining the problems



2 Making assumptions and identifying the variables



3 Applying mathematics to solve problems



4 Verifying and interpreting solutions in the context of the problem



5 Refining the mathematical model



6 Reporting the findings



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The modeling process can be simplified as shown in the diagram below.
Real-world problem

Identifying and Applying Verifying and
defining the mathematics to interpreting solutions
problems solve problems in the context of the

problem

Making Refining the
assumptions and mathematical model
identifying the

variables

Repeat as needed

CHAPTER 8 Reporting the findings

Let us look at one mathematical modeling example that involves all the above components.

Real-world Problem

The grocery store which is far from your house sells a pack of 10 kg rice at a lower price
than the one closer to your house. Is it worth the drive for the cheaper deal?

Identifying and defining the problems
✥ The price of a pack of 10 kg rice and the cost of petrol.
✥ Determine the distance from the two stores to your house respectively.
✥ Find the information needed from the internet, for example the price of a pack of 10 kg

rice from each store, the distance of each store from your house, the current petrol price,
the car’s petrol consumption rate and so on.

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CHAPTER 8 Mathematical Modeling

Making assumptions The assumptions made
usually start with the
✥ The route between the house, store A and store B is a simplest variables.
perfect straight line Once the problem is
solved, more complex
✥ Driving car to the stores assumptions can be
✥ Purchasing the same number and brand of rice at store A considered.

and store B

House Store A Rice Store B Rice

Identifying the variables

✥ Let Memory
• s = the distance between store A and store B Box

• P1 = the price of a pack of 10 kg rice at store A A variable is a quantity
• P2 = the price of a pack of 10 kg rice at store B with an unknown value.
• m = the petrol consumption rate of the car in km per litre

• n = the number of packs of 10 kg rice to be purchased

• H = the current petrol price in RM per litre

• S = the difference in price in RM for purchasing the pack of 10 kg rice at store B as

compared to store A

• T = the difference in the cost of petrol in RM for driving to store B as compared to

store A

Applying mathematics to solve problems

The price of a pack of 10 kg rice
Store A: RM25.95
Store B: RM23.99
Let the quantity of 10 kg rice to be purchased be 2 packs.

The price to be paid
Store A: 2 × RM25.95 = RM51.90
Store B: 2 × RM23.99 = RM47.98

Therefore, by purchasing the rice at store B, one can save
RM51.90 – RM47.98 = RM3.92

Let the distance between store A and store B be 6 km,
the petrol consumption rate of a car be approximately 17.6 km per litre,
the current petrol price be RM2.08 per litre.

Petrol needed for the 6 km route = 6 km = 0.341 litre CHAPTER 8
17.6 km/litre

Cost of petrol for the 12 km (two ways) route = 0.341 litre × RM2.08 ×2 = RM1.42
litre

Therefore, we save RM3.92 – RM1.42 = RM2.50 by purchasing two packs of 10 kg rice at
store B.

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Verifying and interpreting solutions in the context of the problem

The resulting mathematical model is as follows.

S = (P1 – P2) × n

T= s ×H× 2
m

If S . T, then it is sensible to drive to store B to purchase rice and save more money.
If S < T, then we should not drive to store B to purchase rice.

Example of using the model:

S = (P1 – P2) × n T = s ×H× 2 When verifying and interpreting solutions,
= (25.95 – 23.99) × 2 m we consider:
= RM3.92
= 6 × 2.08 × 2 • Are the solutions able to solve the
17.6
problem?

= RM1.42 • Is it rational to translate the solutions to

real-world situation?

Since S . T, you save more money by purchasing rice at store B. Hence it is sensible to
drive to store B. Thus, the mathematical model is able to solve the problem.

From the constructed mathematical model, further exploration can be made.

1. If all the variables remain the same, how far can store Info Bulletin
B be located so that it is an optimum choice?

(P1 – P2) × n . s × H × 2
m
s Optimum means the best
(25.95 – 23.99) × 2 . 17.6 × 2.08 × 2 or the most profitable.

s , 16.6 km

This means that if the distance between the two stores
is less than 16.6 km, then it is sensible to drive to
store B to purchase rice.

2. What is the maximum price of a pack of 10 kg rice at store B that will attract a

person drive to store B to purchase it?

(P1 – P2) × n . s × H × 2
m
6
(25.95 – P2) × 2 . 17.6 × 2.08 × 2

P2 , RM25.24

This means that if the price of a pack of 10 kg rice at store B is less than RM25.24,

then it is worth the trip.

CHAPTER 8 Therefore, the above mathematical model allows us to not only answer the question of “is it
worth it” for the given situation, but also allows us to determine other factors that support or
oppose the decision to drive further to purchase the rice.

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CHAPTER 8 Mathematical Modeling

We now reflect on the model and the questions that arise as follows.

Can we have a Are our assumptions Does this model follow the
negative answer? relevant and assumptions made? Do we need
defensible?
to add more assumptions?

Is this model still valid when we What if our assumptions are
increase or decrease the input wrong? How does that impact

variables? For example, if we keep our answer?
all else constant, but decrease the
value s, the distance between the What if the scenario changes a little?
stores, do we see a decrease in T, Do our results change a lot or a little?
the cost of petrol to travel the extra To what extent do these changes affect

kilometres? the decisions made?

These reflections enable us to think of the needs to refine the mathematical model.

Refining the mathematical model House Store A

The assumption made regarding the route between the house, Store A
store A and store B is a straight line needs to be revised. If the
route between the three places is not a straight line, how does this 2 km
impact our model? If new assumptions are being made, then the
model needs to be revised to reflect this change. 4 km

Reporting the findings Store B

Store B

Use symbols and diagrams when necessary to report the findings. The symbols and
diagrams will depict the whole modeling process until it leads to results. Every model has
strengths and weaknesses. What is important is that the model identifies those strengths and
weaknesses in the report.

For example,
✥ the value of a person’s time is not considered in this model. Is it worth driving an extra

12 km for someone to save RM2.50? According to this model, saving 5 sen is considered
worthwhile.
✥ the model did not account for any environmental considerations. Is it environmentally
responsible to drive an extra 12 km just to save RM2.50? This model did not account for
environmental effort such as efforts to reduce carbon emissions.

We have now seen how the mathematical modeling process works by one example as shown CHAPTER 8
above. We should emphasise that we cannot use this example as a template to solve other
problems. In solving problems through mathematical modeling, every individual or every
group has different ideas, skills and perceptions. Open-ended questions such as these may
even generate completely different mathematical models which are valid yet result in different
answers.

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Example 1 Memory
Box
Jeremy saves RM4 000 at Bank Bunga Raya with a simple
interest rate of 1.5% per annum. Jeremy wants to buy a Simple interest is a reward
computer worth RM4 455 with his savings. How long does given to the depositor
Jeremy need to save? at a certain rate on the
(a) Identify and define the problem. principal amount for a
(b) Determine the assumptions that need to be made and certain period of time.
Simple interest can be
identify the variables in solving the problem. calculated using the
formula I = Prt where I
Solution: is the interest, P is the
principal, r is the interest
(a) In this problem, we know the principal and the interest rate and t is the time in
rate. The interest from the savings is the amount that years.
Jeremy needs besides the RM4 000 to buy the computer.
We need to determine how long Jeremy needs to keep his
savings in the bank.

(b) Assumptions:
• We need to assume that the interest rate does not change during the period of our interest
calculation. Otherwise, the formula I = Prt will not be appropriate.
• We also need to assume that the price of the computer does not change when Jeremy
has raised the required amount of money.

Variables:
The variables involved are I for interest, P for principal, r for interest rate and t for time

in years.

CHAPTER 8 Self Practice 8.1a

1. The journey of a boat moving upstream which covers two places located on the
riverbank takes 6 hours. The return journey of the boat moving downstream takes
5 hours. If the speed of the river current is 2 km h−1, what is the speed of the boat on
calm water?
(a) Identify and define the problem.
(b) Determine the assumptions that need to be made and identify the variables in
solving the problem.

2. In a group, read the question below and find information on the internet.

You have just completed a degree in marketing and received offers to become a
marketing executive by two companies. Company A is in your hometown and offers
a lower starting salary and a lower annual salary increment than company B that is
in a big city. Which is the better choice?

Explain how you use the mathematical modeling process to solve the above problem.

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CHAPTER 8 Mathematical Modeling

How to solve real life problems through mathematical

modeling? Solve real life problems

MIND MOBILISATION 1 Pairs through mathematical
modeling which involves

Aim: To apply mathematics in problem solving. the following functions:
Steps: (i) Linear
(ii) Quadratic

1. Based on the information and diagrams given, determine (iii) Exponential
the type of function (linear, quadratic or exponential) that and communicate the
may be used as a model for the data. mathematical modeling
process implemented.

2. Discuss your selection.

(a) A doctor uses the data to study the resting pulse rate of a normal adult

according to the number of hours of exercise per week.

85Resting pulse rate
80(bpm)
75
70 Population
65
60
55
50
45

Number of hours of

1 2 3 4 5 6 7 8 9 exercise per week

(b) A scientist uses the data to study the population of tigers.

40 000

30 000

20 000

10 000

0 Year

1960 1970 1980 1990 2000 2010 2020

(c) A marketing manager studies the data which shows the relationship between the
profit and the number of years a product is in the market.

Profit, in million 12

10

8

6

4

2

0 1 2 3 4 5 Number of years CHAPTER 8
6


The results of Mind Mobilisation 1 show that we can determine the types of functions that
may be used as a model for data by studying graph patterns.

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Linear function: A graph resembles a straight line. Info Bulletin

Quadratic function: A curved graph in the form of a parabola. The diagram below
The curve may rise and then fall or fall and then rise. shows the graphs of two
exponential functions
Exponential function: A curved graph y with base e where
illustrating an increase or decrease in values e = 2.7182818284
of data at a sharp rate. The exponential y = 2x
function can be written in the form of y
equation y = Cax, where a is a positive real 1
number, a ≠ 1 and C is an initial value. For Ox y = e–x y = ex
example, if C = 1 and a = 2, graph y = 2x is
shown as the diagram. 1
Ox

Example 2

Amin travelled 405 km on 45 litres of petrol in his car. If Amin wishes to go to a place
which is 198 km away by car, how much petrol, in litres, does he need? Solve this problem
through mathematical modeling.

Solution:

Identifying and defining the problem

• Determine the volume of petrol required for 198 km.
• We know that the farther we travel, the more petrol we require. Thus, the amount of petrol

varies directly with the distance we travelled.

Making assumptions and identifying the variables

• Assume that the driving speed for both 405 km and 198 km routes are the same
• Let x represents the distance travelled and y represents the amount of petrol required
• y varies directly with x, hence y = kx where k is a constant

Applying mathematics to solve problems

Substitute y = 45 and x = 405 into y = kx,

4 5 = k (405)

k = 45 = 1
405 9

Therefore, y = 1 x
9

This equation describes the relationship between the amount of petrol required and distance
travelled.

CHAPTER 8 When x = 198, y = 1  (198)
9

= 22 litres

Hence, 22 litres of petrol is required to travel 198 km.

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CHAPTER 8 Mathematical Modeling

Verifying and interpreting solutions in the context of the problem

We may not be able to use the linear function model y = 1 x in all y
9
situations. For example, if the 405 km route is through towns and cities,
y = 1 x
and the 198 km route is through highway. Thus, the car will use up petrol 9

at a faster rate in the first route compared to the second route. When this O x

is translated to the real-world situation, the linear function model obtained

is not suitable to solve this problem.

Refining the mathematical model

In this problem, we are not able to refine the model due to limited information given.

Reporting the findings

Report the findings of the problem solving based on the interpretation of solutions as shown
in the preceding sections.

Example 3

The diagram below shows the cross section of a river. A hydrologist measures the depth of
the river, y m, at different distance, x m from the riverbank. The results obtained are given in
the following table.

Distance from the Depth of the
riverbank, x m river, y m
0 0
4 1.5
8 2.3
12 2.9
18 2.9
25 1.7
30 0

Show how the hydrologist uses the data above to determine the depth of the river through
mathematical modeling.

Solution:

Identifying and defining the problem Ap&plicCatairoener

How to determine the depth of the river? A hydrologist is a CHAPTER 8
scientist who researches
Making assumptions and identifying the variables the circulation,
distribution and quality of
• Assume the river is the deepest in the middle with the water in an environment.
depth decreasing to 0 at the edges.

• The two variables involved in this study are the depth of
the river, y m, and the distance from the riverbank, x m.

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Applying mathematics to solve problems y (15, 3.0)
3.2
• Write the distance from the riverbank and the 2.8
depth of the river as a set of ordered pairs 2.4
(x, y) and draw a graph for the data. 2.0
1.6
• The data seem to rise and fall in a manner 1.2
similar to a quadratic function. 0.8
0.4
• The graph drawn shows the curve of best fit and
resembles the graph of a quadratic function.

• In mathematical modeling to represent the
actual situation, the approximate value is used.

• Based on the graph, the depth of the river is
3 m when the distance from the riverbank is
15 m (approximate).

0 4 8 12 16 20 24 28 x

Verifying and interpreting solutions in the context of the problem

Determine the related quadratic function of the form y = ax2 + bx + c. Determine the
constants a, b and c by substituting any three data, for example (0, 0), (25, 1.7) and (30, 0)
into the equation.

0 = a(0)2 + b(0) + c 0 = c
1.7 = a(25)2 + b(25) + c 1.7 = 625a + 25b + c

0 = a(30)2 + b(30) + c 0 = 900a + 30b + c

Since c = 0, the system of two linear equations in two variables is:

1.7 = 625a + 25b ......................... a

0 = 900a + 30b ......................... b  Info Bulletin

From b, b = −30a ....................... c A system of linear
equations refer to two
Substitute c into a, 1.7 = 625a + 25(−30a)
or more linear equations
1.7 = −125a involving the same set of
a = −0.0136 variables.

Substitute a = −0.0136 into c, b = −30(−0.0136)

= 0.408

Hence, the possible quadratic function is y = −0.0136x2 + 0.408x

Substitute x = 15, y = −0.0136(15)2 + 0.408(15)

= 3.06 (approximate to the answer obtained from the graph)

CHAPTER 8 Refining the mathematical model

• For this model, we assume that the river is the deepest in the middle. This may not be true
for some other rivers. A new model will be needed if we have new assumptions.

• The answer will be more accurate if more data have been collected.

Reporting the findings
Write a full report following the above modeling framework structure.

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CHAPTER 8 Mathematical Modeling

Example 4

Compound interest is interest that is calculated based on the original principal and also the
accumulated interest from the previous period of savings. At the beginning of a year, Mr
Gomez saves RM20 000 in his savings account with an interest rate of 4% per annum and
the interest is compounded once a year. Derive a mathematical model for Mr Gomez’s total
savings after t years of saving. Solve this problem through mathematical modeling.

Solution:

Identifying and defining the problem

• Mr Gomez is given compound interest which is compounded once a year.
• His principal is RM20 000.
• The yearly interest rate is 4%.
• Derive a mathematical model for Mr Gomez’s total savings at the end of t years.

Making assumptions and identifying the variables

• Assume Mr Gomez did not withdraw or raise his savings throughout the period of saving.
• The variables are principal amount, RMP, yearly interest rate, r, number of times the

interest is compounded, n, and time, t years.

Applying mathematics to solve problems

Keep in mind that when calculating the compound interest, each year we have 100% of the
principal, plus 4% of the previous balance. We construct a table as follows.

Year Principal Interest received Principal + Interest Amount of
(RM) (RM) (RM) savings (RM)
20 000(1.04)
1 20 000 20 000 × 0.04 20 000 + 20 000 × 0.04
= 20 000(1 + 0.04) 20 000(1.04)2
2 20 000(1.04) 20 000(1.04) × 0.04
20 000(1.04) + 20 000(1.04) × 0.04 20 000(1.04)3
3 20 000(1.04)2 20 000(1.04)2 × 0.04 = 20 000(1.04)(1 + 0.04)
20 000(1.04)4
4 20 000(1.04)3 20 000(1.04)3 × 0.04 20 000(1.04)2 + 20 000(1.04)2 × 0.04
= 20 000(1.04)2(1 + 0.04) 20 000(1.04)5
5 20 000(1.04)4 20 000(1.04)4 × 0.04
20 000(1.04)3 + 20 000(1.04)3 × 0.04
= 20 000(1.04)3(1 + 0.04)

20 000(1.04)4 + 20 000(1.04)4 × 0.04
= 20 000(1.04)4(1 + 0.04)

Verifying and interpreting solutions in the context of the problem CHAPTER 8

Based on the table above, at the end of every year, the amount of savings is a power of 1.04
times the principal, RM20 000, and the power corresponds to the number of years of saving.

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We can generalise this pattern to a mathematical model by letting P represents the principal
of the savings, t represents the number of years, and r represents the yearly interest rate.
Hence, the mathematical model is

A(t) = P(1 + r)t, Note that 1.04 = 1 + 0.04 = 1 + r

where A(t) is the amount of savings after t years. Amount of savings, A(t) (RM) 100 000 A(t) = 20 000(1.04)t
80 000
This mathematical model is an exponential 60 000
function that allows us to calculate the amount of 40 000
savings if the interest is compounded once a year 20 000
for t years.

The graph on the right shows an exponential
function A(t) = 20 000(1.04)t. The graph of the
amount of savings after t years, A(t), shows an
exponential growth as time, t, increases.

Refining the mathematical model

The mathematical model A(t) = P(1 + r)t is used 0 10 20 30 40
for annual compounding. In reality, interest is Time, t (years)

often compounded more frequently, for example, compounded semi-annually or quarterly.

If the interest is compounded monthly, the interest rate r is divided amongst the 12

months because 1 of the rate is applied each month. The variable t in the exponent
12

is multiplied by 12 because the interest is calculated 12 times in a year. Hence, the

1 2mathematical model becomes A(t) = P  1 +r 12t. In general, if the interest is compounded n
12

1 2times per year, the mathematical model is A(t) = P  1 +r nt.
n

Reporting the findings

Write a full report following the above modeling framework structure.

CHAPTER 8 Self Practice 8.1b

1. A runner is training for a marathon, running a total of 32 km per week on a regular
basis. The runner plans to increase his running distance D(x), in km, each week by 10%,
where x represents the number of weeks of training. Derive a mathematical model for
his running distance, D(x). Solve this problem through mathematical modeling.

2. Hyperthermia is a condition where an individual’s body temperature is elevated beyond
normal. Causes of hyperthermia include dehydration, an excessive loss of body fluids.
Why the risk of hyperthermia higher among young children compared to adults in hot
weather? Investigate this problem through mathematical modeling.

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KPM